Question: Solve for $a$ : $5 + a = 4$
Subtract $5$ from both sides: $ \begin{eqnarray} \\ 5 + a &=& 4 \\ \\ {-5} && {-5} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{5 + a} &\hphantom{=}& \hphantom{4} \\ a &=& 4 {- 5} \\ \end{eqnarray} $ Simplify. $ a = -1$